Whether childhood cancer is becoming more common is a controversial question among scientists.
Data from the cancer tracking systems in the US suggest that childhood cancer is increasing. The tracking systems record new cases of cancer in some areas of the US. The largest tracking system is called SEER and is funded and overseen by agencies in the federal Department of Health and Human Services.
The National Cancer Institute and other agencies use the tracking information from SEER to try to determine whether childhood cancer is increasing.
In 1996, the National Cancer Institute reported that the frequency (incidence rate) for cancer of all types in children increased 10% between 1973 and 1991. This means that 10% more new cases of cancers per million children were found in 1991 than in 1973. During this period, brain cancer and soft tissue sarcoma each increased more than 25% (1).
In 1999, the National Cancer Institute reported that this increase in childhood cancer appeared to have leveled off after 1990 (2).
Click here to see a graph of trends in childhood cancer in the 1970s to 1990s.
One reason that it is difficult to tell for sure whether rates are increasing is that changes are not consistent from year to year. For example, the frequency of all childhood cancer cases in 1995 was higher than 1994 for boys but lower than 1994 for girls.
To look at trends, it is also important to look at differences for individual forms of cancer and not just for the overall cancer rate.
NCI reported that, for infants less than one year old, the cancer rate increased from 197.9 cases per million infants during the years 1976-84 to 264 cases per million infants during the years 1986-94. This was a 36% increase (3). The greatest percentage increase occurred for germ cell cancers (increase of 124%), central nervous system cancers (increase of 57%), liver cancers (increase of 50%), and neuroblastoma (increase of 35%).
In its monograph reporting these increases, the National Cancer Institute comments that these increases may be due to a variety of factors such as improved detection, rather than representing true increases in cancer (3).
While the tracking system are showing that more cases of childhood cancer were found in 1990 than in the 1970's, different people interpret this reported increase in different ways. Some people believe that the reported increase in the number of cases reported do not represent real increase in disease.
There are several reasons why the number of new cases of a disease may go up.
One, of course, is that the disease may become more common. This would be a "real" increase in disease.
However, the number of cases of a disease could also go up if people's access to medical care increased, so that more people got tested for the disease, and more cases were found.
A third reason that number of cases reported could go up is if better methods or technologies are adopted so that cases are found that would have otherwise not have been detected.
A fourth reason is that sometimes the way that doctors define disease changes, so that more types of tumors may be counted as cancer, for example.
Scientists disagree about which of these reasons apply to the increase in cancer in children.
Many scientists believe that the increases reported reflect a real increase in disease. Dr. Phil Landrigan of the Mt. Sinai Hospital of New York says that almost all cases of brain cancer are found, so the changes in technology cannot be the reason that the disease is found more often (4).
Other scientists disagree. For example, scientists from the National Cancer Institute have argued that all of the increases in brain cancer in children are because new methods are better at detecting the cancer than those used in earlier years (5, 6).
Another way to measure changes in cancer is to look at the mortality (or death) rate. This counts the number of people in a group that die from a disease over a defined period, usually a year. Mortality rates are generally influenced by the effectiveness of medical treatments. If many people get a disease but the treatment is very effective, only a few will die. In this example, the mortality rate will be low even though the incidence rate is high.
One area of very good news related to childhood cancer is that treatments for many cancers have improved greatly over the last few years. As a result, mortality rates are generally going down.
From a statistical point of view, this means that mortality rates are not a good way to keep track of how common childhood cancers are.
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1. NCI. Cancer Rates and Risks, Fourth Edition: National Institute of Health, National Cancer Institute, Division of Disease Prevention and Control, Cancer Statistics Branch, NIH Publication No. 96-691, 1996.
2. Ries LAG, Smith MA, Gurney JG, Linet M, Tamra T, Young JL, Bunin GR, eds. Cancer Incidence and Survival Among Children and Adolescents: United States SEER Program 1975-1995. Bethesda, Md.: National Cancer Institute, SEER Program, 1999.
3. Gurney JG, Smith MA, Ross JA. Chapter 12: Cancer among infants. In: Ries LAG, Smith MA, Gurney JG, Linet M, Tamra T, Young JL, Bunin GR, eds. Cancer Incidence and Survival Among Children and Adolescents: United States SEER Program 1975-1995. Bethesda, Md.: National Cancer Institute, SEER Program, 1999:149-157.
4. Kaiser J. No meeting of minds on childhood cancer. Science 1999; 286:1832.
5. Smith MA, Freidlin B, Ries LA, Simon R. Trends in reported incidence of primary malignant brain tumors in children in the United States. Journal of the National Cancer Institute 1998; 90:1269-77.
6. Smith MA, Freidlin B, Ries LA, Simon R. Increased incidence rates but no space-time clustering of childhood astrocytoma in Sweden, 1973-1992: a population-based study of pediatric brain tumors [letter]. Cancer 2000; 88:1492-3.
